1. Technical Field
The present invention relates to a sizing agent for carbonizable fiber and a method for manufacturing carbon fiber with the sizing agent.
2. Prior Art
In the course of manufacture of carbon fiber, the fiber is liable to undergo napping due to contact with guide rolls and so on.
To prevent napping, therefore, a flame-resistant fiber (such as an oxidizing acrylic fiber) or non-fusible fiber (such as a graphitizing infusible pitch fiber) is generally coated with a sizing agent prior to carbonization (Japanese Patent Publication No. 64-6288).
As sizing agents, there has been proposed a variety of water-soluble materials such as starch, processed starch, dextrin, amylose, carboxymethyl-cellulose, polyvinyl alcohol, water-soluble polyurethane resin and so on.
However, these hitherto-known sizing agents have one or more of the following disadvantages, viz. (1) poor solubility in water, (2) a too stiff film produced, (3) not easily decomposed on heat treatment, (4) large amounts of ash remain which as an impurity detrimentally affect the physical properties of the carbon fiber.